Differential dependence of hypoxia-inducible factors 1 alpha and 2 alpha on mTORC1 and mTORC2.
Constitutive expression of hypoxia-inducible factor (HIF) has been implicated in several proliferative disorders. Constitutive expression of HIF1 alpha and HIF2 alpha has been linked to a number of human cancers, especially renal cell carcinoma (RCC), in which HIF2 alpha expression is the more important contributor. Expression of HIF1 alpha is dependent on the mammalian target of rapamycin (mTOR) and is sensitive to rapamycin. In contrast, there have been no reports linking HIF2 alpha expression with mTOR. mTOR exists in two complexes, mTORC1 and mTORC2, which are differentially sensitive to rapamycin. We report here that although there are clear differences in the sensitivity of HIF1 alpha and HIF2 alpha to rapamycin, both HIF1 alpha and HIF2 alpha expression is dependent on mTOR. HIF1 alpha expression was dependent on both Raptor (a constituent of mTORC1) and Rictor (a constitutive of mTORC2). In contrast, HIF2 alpha was dependent only on the mTORC2 constituent Rictor. These data indicate that although HIF1 alpha is dependent on both mTORC1 and mTORC2, HIF2 alpha is dependent only on mTORC2. We also examined the dependence of HIF alpha expression on the mTORC2 substrate Akt, which exists as three different isoforms, Akt1, Akt2, and Akt3. Interestingly, the expression of HIF2 alpha was dependent on Akt2, whereas that of HIF1 alpha was dependent on Akt3. Because HIF2 alpha is apparently more critical in RCC, this study underscores the importance of targeting mTORC2 and perhaps Akt2 signaling in RCC and other proliferative disorders in which HIF2 alpha has been implicated.
Toschi
Alfredo
A
Department of Biological Sciences, Hunter College, The City University of New York, New York, New York 10021, USA.
Lee
Evan
E
Gadir
Noga
N
Ohh
Michael
M
Foster
David A
DA
D048868:Adaptor Proteins, Signal Transducing; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008954:Models, Biological; D046912:Multiprotein Complexes; D011506:Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism*; D000099162:Endothelial PAS Domain-Containing Protein 1
D048868:Adaptor Proteins, Signal Transducing; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D011506:Proteins; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C492571:RICTOR protein, human; C463659:RPTOR protein, human